Ener-G egg replacer works well for cookies since cookies are meant to be flat, but it's not so great for brownies or cake which generally get most of their fluffy airiness from eggs. You might want to look into some vegan cookbooks -- they usually have interesting combinations of ingredients to mimic the effect that eggs produce (soy milk + vinegar is one such trick.) Check out Isa Chandra Moskowitz's books. Good luck!